R365, a solvent and precursor for other chemicals, is a by-product formed during the manufacture of R141b, a replacement for trichlorofluoromethane as a blowing agent, and 1-chloro-1,1-difluoroethane ("R142b"), a key intermediate in the production of polyvinylidene fluoride, by the liquid phase hydrofluorination of 1,1,1-trichloroethane, as described, for example, in EP 297,947. While R365 is generated in small amounts, typically about 0.5 weight percent based on the amount of R141b product, R365 and R141b have similar boiling points (40C and 32C, respectively) and form an azeotrope having a composition of about 19 mol % R365 and 81 mol % R141b, making separation by conventional distillation means extremely difficult.
While liquid-liquid solvent extraction techniques have been disclosed, as in U.S. Pat. No. 4,031,148, the introduction of substances foreign to the manufacturing process is undesirable since they would require extensive post-extraction purification and solvent recovery.
Thus, what is needed is a method for the removal of R365 from R141b which is efficient and, preferably, compatible with the manufacturing process.